Yes ELVs <50Vdc.  IMHO its sheer madness to be involved with MV dc Panel strings - way too dangerous  IMHO in a domestic environment, and we dont have the skilled tradesmen to recognise this type of micro grid nor is there a recognised route to upgrade to this unfamiliar but hazardous system.  Way too many unschooled wannabees playing with fireworks.  It is utter negligence by our Political leaders to allow this to continue.  They only woke up to the hazards of amateur plumbers who didnt understand flammable atmospheres till a few houses were blown up flattened.  Then British gas had to step in a institute proper training courses with local tech colleges.  Where do our Electricians get proper upgrades?  A one man jobber cant afford an apprentice (with all the paperwork and oversight involved). He will only have a family member or friend involved.

mapj1 said:

To my mind the error  of modern society is to infantalise the 'consumer' and assume they are incapable of understanding and making any technical decision as if consumers are some blobby mass incapable of doing  anything more complex than signing a cheque,.

Not sure what that has to do with what we're talking about?

For example, is it OK to put gg type fuseholders in accessible places on battery storage systems in homes that can be simply "pulled on load" by anyone ... including children? Similarly, sitting series/parallel monoblocs without internal overcurrent protection on the floor (for example in the garage or even on boards in the loft)??

Because that's what's happening in some ("not amateur") installs?

And an educated customer or a customer who's friends felt able to offer an opinion would pick up on this and say 'that's not right' much as we all know helpful folk who will tell you that your car has a problem - even if as in  my case you already know.

Thus the wider educated collective can correct - being a far better policeman than some trade body that looks at a few jobs a year that are within a short drive and easy to look at, where a large part of their aim is to keep the subscription payment flowing.

Mike.

mapj1 said:

And an educated customer or a customer who's friends felt able to offer an opinion would pick up on this and say 'that's not right' much as we all know helpful folk who will tell you that your car has a problem - even if as in  my case you already know.

Thus the wider educated collective can correct

I do take that point in general. But that doesn't appear to be happening with Solar & Battery installations.

I was astonished to see a well known US brand which supplies a complete solar kit down to the inverter mains outlet use a rotary cam switch (typically seen on electrical panels) as a circuit breaker between the panels and the Inverter  (no internal arc quench in that design).

A simple rotary isolator between PV panels and inverter is a pretty well accepted way of doing things. It's only intended as an off-load isolator to allow work on the inverter. PV panels, unlike mains or large battery supplies, are incapable of producing large currents (it's limited by sunlight) - even into a dead short the maximum expected is 125% of normal output current. Oversize your PV d.c. cables by a little and no overcurrent protection is needed in a simple system.

Introducing batteries does introduce the potential for much nastier problems of course, but the charge controller would usually prevent backk-flow from the battery to the panel circuit.

   - Andy.

AJJewsbury said:

even into a dead short the maximum expected is 125% of normal output current

That's more than sufficient current to draw an arc, and sustain it for some considerable period of time (for example as an MC4 burns and disintegrates). WIth currents as low as 1-2 amperes !

In fact, if there is a fault, because they do happen, what is built into a solar PV system to enable someone to work on the system safely, or remove the arc etc.? Usually nothing!

For safe working on Solar PV, isolating at the inverter may stop current flow ... but what are the consequences if it didn't (say because there's a fault L+ to L- between the panels and in the inverter)? The only way to check for this, is to check for DC current flow with a DC current clamp meter at the point of disconnection, prior to disconnecting (because there's nowhere to "prove dead").

If not, these are the potential consequences: youtu.be/rkq1zwG9vLc

gkenyon said:

It's possible to cause an arc at 12 V DC

WRONG more homework needed GK

https://www.youtube.com/watch?v=5FXRuT6TU2U

you cannot draw an arc flash at 12 Vdc - nor at 15Vdc from a battery charger - its the Physics of the subject (very esoteric)

Here is an example with 2 batteries 24Vdc

https://www.youtube.com/watch?v=PV5oLPLUzrM

An arc flash can be sustained (out in the bush people have used coat hangers as welding rods)

Note the size of the Arc Flash and imagine that sustained in your faulty breaker or fuse holder

What will you do next ?

Are emergency procedures stuck to the wall for Joe Public and his Family?

gkenyon said:

For safe working on Solar PV, isolating at the inverter may stop current flow ... but what are the consequences if it didn't (say because there's a fault L+ to L- between the panels and in the inverter)? The only way to check for this, is to check for DC current flow with a DC current clamp meter at the point of disconnection, prior to disconnecting (because there's nowhere to "prove dead").

Indeed, a good point raised here - how to tell if a dc cable is dead.  Analogy the ubiquitous neon screw driver owned by every Leccie, automatically check for a live wire before intervention (also the bare knuckle test some believe is more reliable as your neon could fail)

So what is proposed here is that compulsory use of a Hall Effect clamp meter on solar cables before intervention.

BUT  the sad thing here which my OP highlighted is that we dont have any formal training worth a damn to promote theis level of Safety Training

I agree it isn't but then where is the public information on what to look for ?

That absent  public profile again - Rather like how to check your tyres or oil, how to see if your electrics look dicky... It would not be hard. Perhaps it is a pity the old scary safety film unit is no longer in operation...

(I did wonder if British Public information films of kids being hit by trains and tractors or being accidentally locked in fridges and other such stuff were a side effect of the film classification system being quite strict, so frustrated British horror film makers ended up doing things like The Apaches or The Finishing line instead where they could let rip in the name of education. What they could have done with an unprotected  DC supply I wonder ? )

Mike

Rob Tes said:

WRONG more homework needed GK

I think we are at odds only in terminology, and I have tried to explain that in a previous post. To sustain the arc is difficult with 12 V due to the very short distance necessary. Easier with carbon or carbonised metal ... I never said you can weld with 12 V using arc welding sticks ... but arcs can be drawn for short periods with 12 V if you know how

youtu.be/Frk3M38mfl4

Perhaps rudeness is not necessary.

Rob Tes said:

you cannot draw an arc flash at 12 Vdc - nor at 15Vdc from a battery charger - its the Physics of the subject (very esoteric)

Yes, arc flash energy at 12 V may well be low, but an "arc" is not "arc flash" - they are two different things.

An arc can lead to arc flash (or not).

Rob Tes said:

BUT  the sad thing here which my OP highlighted is that we dont have any formal training worth a damn to promote theis level of Safety Training

Agreed ... not everyone has the relevant training and experience.

Rob Tes said:

BUT  the sad thing here which my OP highlighted is that we dont have any formal training worth a damn to promote theis level of Safety Training

Agreed ... not everyone has the relevant training and experience.